Heater for fluids



Dec. 27, 1938. o. woLF ET AL I HEATER AFOR ELUIDS v Filed Jly 6, 1955 2 Sheets-Sheet 1 Q i W g v-i t I 0 m Q Q N u ,"5 Ll. w D

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BY /ZNZENTOR Dec. 27, 1938.

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Q WOLF ET AL 2,141,633

HEATER FOR FLUIDS Filed July 6, r1955 sheets-sheet 2 .am/MM" /he/'r ATTORNEY Patented Dec.v 27, 1938 PAT ENT OFFICE assignors to The vTexas Company, New York, N. Y., a corporation of Delaware Application July 6, 1935, Serial No. v30,123

. 4 :'4 claims. This inventionrela'tes toa new 'type furnace and heater for heating hydrocarbon Ymaterials,

such'as crude oil or petroleum Sdistil1ate,`to ternlperatures upwardrof i4800 Itis a primary object of fthe invention to provide-aheater which lwill have a higher eicien'cy lin operation and be of `smaller 'proportions' for `the sameheat transfer capacitylthanthose here- 'tofore available. lo The `greater eiciencyincperation 4is attained in part `Vby maintaining .a :substantial positive pressure in the combustionand heat absorption sections of 'the furnace Aand 'by re'circulating a portion of the exhaustgasesunderpressure with 1]'5 the new products oflcombustion passing the heat absorption tubes so as Lto equalize the heat absorption inthe radiant and convection sections of y'the heater.

' The'invention -will`=be full-y understood from the T20 following description 4when considered in connection Awith thedrawings, in -which,-

Fig. l illustratesthe'essential/features lof one fform which the present invention Imay assume.

Fig. 2i1lustrates a modified form of 'furnace :'25 'and heater.

The heater'includes a-vessel of-general cylin- `drical or rectangular'crosssection and having an enlarged-central section-'B constituting the radiant heat absorption section, a reduced section 30 `8 `at oneend, constituting a combustion section 'and 'a reduced section VIU at 'the opposite end constituting the convection heat absorption section.

The-section V6 is preferablyformed rwith a sin- :3'5 glebank ofc'losely sp'acedtubes I`2'encircling the same, the tubes l2 preferably extending through the lfurnace -walls and-being connectedby return bends placed outside the-furnace chambers. The ends 'of the tubes are enclosed within channels 401:3 secured to the furnace Walls. This construction is not essential'but is preferred so that the int'eriorof rthe furnace may be sealed, with the Ytubes l2 loosely mountedin thelopenings in the "furnace .wa11, permitting independent contrac- 14'5 tion "and expansion of the Ttubes and furnace Walls. In the particular construction disclosed Vherein lthe radiant section Vis v'provided with y'40 lto50 closelyspaced' tubes,"4 1/2 'inches rin diameter and 20 ffeet long, vexposed Vfor their entire 'length' 50 and-spaced inwardly from'the furnacewall.,

The tubes TI'4 lin the convection section l0 are closely spaced and occupyka `'rnajor portion of fthe' entire VVolumey of the section. shown, vthere Hare'approximat'elythirteenparallel :rows of tubes,l .g5 'each tub'e fhavinglfaidiameter `of :451,5 :inches @with a clearance of -one-half inch between the pipes. With a convection section `having 'a cross sectional area nof approximately 25 square feet, lthiswillfaiford slightly less than 1000'square'lfeet `of pipe surfacel exposed `to the heated. gases. :f5 Since'the front'rows of pipes in 'theconvection section vwill be 'exposed to 'the radiant heat yof `the 'burnen-it "isi preferred itc-.space the first few rows vof lpipes to agreater extent ythan in .the Jmainibank of `pipes Iltin the section. V'I'his forms im a shield section subjected to lower mass :velocities of the 'passing gases 'to .compensate for the direct furnace radiation received .'by these exposed pipes. f

The tubes in the 'convection'fsection are posiam tioned closely together for 'the dual purpose of "obstructing the flow of gases, for `maintaining in `the furnace the desired pressure, vand for the further purpose of providing a'high mass velocity of gases contacting the convection tubes 7,20 for achieving 'a greatly increased heat transfer' rate from the combustiongases to the material passingvthrough the tubes.

It will be understood that the arrangement, size and form ofthe tubes in the radiant and 25 convection fsections will bel selected in accordance withthe particular installation being made V'and that wide variations in 'these vrespects are l'permissible. In the present adaptation of the invention the charge is introduced into the fur- ..30 nace in the convection .section `asfindicated at I6, .passingfin series through the tubes in the convection section, then through the tubes in the yradiant section, being Jnally discharged kas indicated at I8. Y 535 The burnerfor supplying fuel and fair to the combustion -section 8.of the furnace 'may be of 'any desired type (not shown). The fuel supply 120 and air supply 22 are maintained under substantial pressure, corresponding to the kpressure 40 desired to be maintained in the furnace, as `indicated below.

Thefgas streamipassing from the convection section-of the furnace is divided insuch .a pro- :portion that an amount of gas corresponding 345 to the fue] gasplusicombustion air is directed to a gas turbine while a portion of the gases are Vrecirculated through the furnace Vwith the `ignited gases from-the burner. The compressed lheated gases discharged from the heater kconsti- 50 tute a satisfactory source of power forv compressing the "recirculation .gases and alsoA for compressing the new combustion promoting Yair `introduced under pressure Yinto the furnace. The :turbine can also befutilizedlforfcompressing fthe 55 fuel although in most instances the -fuel is supplied to the burner under such initial pressure that further compression is unnecessary.

The gas stream discharged from the convection sectio-n of the heater at 24 is accordingly divided, a portion going through the conduit 26 to the gas turbine 28 and a portion Vthrough the pipe-30 to the compressor 32. The turbine 28 may be of any standard construction utilizing the compressed heated exhaust gases and serving to drive the power shaft 3 at a predetermined speed. The compressor 32 may also be of any standard construction although a centrifugal compressor is preferred due to the largeY Volume of gases which the compressor must ace commodate. The gases compressed at 32 areV passed through the conduit 35 into the heater at suitable points indicated at 36, the gases being thereby recirculated through the entire heat absorption section of the furnace with the. new products of combustion produced at the burner.

In order to withdraw as much as possible of the sensible heat from the discharged gases, these gases are passed through a heat exchanger 40 before being discharged throughY the stack 4|. The air supplied to the furnace at 22 is compressed by a compressor 38 which forces the compressed air through the heat exchanger 40 countercurrent to the ow of exhaust gases, the heated air being conducted to the burner through the lines 22. Y

The shaft 34 may be operated initially or in emergency by the motor 44, this motor being automatically disconnected from the shaft in the normal operation of the furnace after temperatures and pressures have been reached.

In theY modified form of the apparatus the principle involved in the construction is the same except that a double ended heater is employed wherein fuel is introduced at both ends of the vessel and discharged on one or more sides adjacent the central portion of theA vessel. This is illustrated in Fig. 2 wherein the vessel 50 is formed with two combustion sections 52 and 54 to be provided with the usual'burners (not shown) for receiving fuel and airV injected into the vessel under pressure. The central section 56 of the vessel is provided with tubes'58, preferably,

placed in a Vsingle row around the interior of the vessel and extending for the entire length thereof except at the entrance to the convection section 50 leading to the outlet 62. This section is filled 'A with closely spaced tubes (ilV between which the hot gases pass as in the rst form of the inven-V tion. Y Y.

The charge Vto be heated in the tubular furnace is introduced into the tubes in the convection section as indicatedV at 15a, the charge passing from the convection section to and through the tubes rcomprising the radiant section and out through the passageia.. It is preferred to pass the charge inseries through the entire YsetV of tubes in the convection section and then in the radiant section although it will be understood that the heater may be made suiciently large that the tubes may be divided to provide two or more parallel passagesY for the material being heated.

YThis latterconstruction would be particularly desirable incase two duplicate sections 00 and ldischarge passages 62 are employed, .on opposite sides of the central portion of the furnace. The remaining elements of the system,including the gas turbine, compressors, preheat apparatus for the air, etc., connected withrthe corresponding conduits 20a., 22a, 24a and 34a, will be the same as in the first form of the invention so that it is unnecessary to duplicate these features of construction in Fig. 2.

Inthe normal operation of the system, assuming a desired temperature of approximately 900 F. in the gas stream passing from the convection section, it is contemplated to maintain in the combustion space of the vessel 4 a pressure of from 25 to 35 pounds per square inch absolute although the system can be operated with any pressure substantially above atmospheric, for example, 15 pounds'per square inch absolute up to 50 pounds per square inch absolute.

The flue gases after passing through the turbine will have dropped to a temperature of from 600 to 650 F. and will be only slightly above atmospheric pressure', for example, 14.8 to 17 pounds g absolute. lThis temperature is sunicient 4to ob- Y tain an appreciable air preheat in the heater d0 The preferred pressure to be maintained in the interior'of the furnace is from 28 to 30 poundsr absolute. lThis requires a relatively heavy walled (furnace, carefully jacketed so that no leaks occur where the tubes pass through the walls of the furnace, for example. Theinterior of the furnace should be lined with a relatively heavy insulating material to protect the metal walls and the exterior surface adequately insulated to prevent undue loss of heat.

It has been found that the absorption of heat in the radiant section can be reduced to a quantity such that asubstantially equal number of heat units are absorbed in the radiant and convection sections of the furnace by recirculating a portion of the exhaust gases through the heater. It issuiiiCient to recirculate from 10% to 50% of the exhaust gases, approximately 30% being preferred for most operations. These exhaust gases serve to limit the heat absorption in the radiant tubes and to forward additional heat units for absorption in the convection section. Since the ue gas is recirculated Vsubstantially at its discharge temperature of 900 F.,

there is little ultimate heat loss in recirculating these gases through the furnace, assuming all conduits to Ybe properly jacketed.

TheV construction disclosed herein is based uponV a flow Vof combustion gases of the order of 16 pounds per second. There is a free area between the tubes in the convection section disclosed of Y approximately 2 square feet, giving a mass velocity in the convection section of about 8 pounds, per square foot, per second. A mass velocity of from 4 to 6 pounds is readily attainable with a construction of the type disclosed. 'Ihese values are considerably higher Ythan are attainable with the usual type heater and materially increase the heat absorption in the convection section.

, Y With the furnace described herein a greater overall efficiency is att-ainable than with the pres.-

ent conventional furnace design operating at lowV Vvmore rapid combustion reactions -atthese high ffurnace' pressures, witha higherstate oftur- 75 bulence and shorter flame length. The danger of direct flame impingement on the tubes in the radiant section is practically avoided. Due to the positive control of all of the elements affecting combustion conditions in the furnace, including the recirculation of a portion of the exhaust gases, there is an increased operating ilexibility adapting the construction to various requirements with a minimum of structural change.

It will be understood that suitable valves and other controls are provided for the various units and conduits of the apparatus in order to attain the desired operation, including temperatures and pressures throughout the system.

Obviously, many other modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In a furnace, a combustion vessel, means for introducing fuel and combustion promoting gas under pressure into said vessel, means for passing hydrocarbon fluids in indirect heat conducting relation to the interior of said vessel for heating said fluids and for maintaining pressure above 25 pounds per square inch absolute in said vessel, a power mechanism, means for utilizing spent exhaust gases discharged from said vessel for actuating said power mechanism, means for compressing combustion promoting air by said power mechanism, and means for compressing a portion of said spent exhaustgases by said power mechanism' and reintroducing same into said vessel for diluting the combustion gases therein.

2. The method of operating a uid hydrocarbon heater having a radiant heat absorbing section and a convection heat absorbing section comprising introducing fuel and combustion promoting air into the combustion space of said heater near said radiant section and discharging gases therefrom while maintaining the combustion space under pressure of from 25 to 35 pounds per square inch absolute, heating said hydrocarbons by indirect heat transfer from said heated gases, compressing a portion of the heated exhaust gases discharged from said combustion space and reintroducing the s-ame under pressure into said combustion space to control the relative amounts of heat absorbed by said radiant and said convection sections.

3. In a furnace, a combustion Vessel, means for introducing fuel and combustion promoting air into said vessel, a radiant heat absorbing section and a convection heat absorbing section in said vessel, means for passing hydrocarbon uids rst through said convection section and then though said radiant section so as to absorb heat indirectly from the interior 'of said vessel, a power mechanism actuated by a portion of the exhaust gases discharged from said vessel, means operated by said power mechanism for compressing the remaining portion of said exhaust gases and for reintroducing the compressed exhaust gases into said vessel to modify and control the relative heat absorption of said radiant and convection heat absorbing sections.

4. The method of heating uid hydrocarbons in a furnace comprising igniting fuel and combustion promoting air in the combustion space of the furnace, maintaining said combustion space under pressure of from 25 to 35 pounds per square inch absolute, indirectly heating said hydrocarbons by radiant heat from the ignited fuel in the vicinity of said ignited fuel and by convection heat at a position remote from said ignited fuel while retarding the flow of gases from said combustion space for maintaining positive pressure therein, utilizing a portion of the exhaust gases discharged from the combustion space to compress the remaining portion of the exhaust gases discharged from the combustion space, and reintroducing said compressed exhaust gases into the combustion space to control the relative amounts of the radiant and convection heat absorption.

OSCAR WOLF. ROSS C. POWELL. 

